1. Field of the Invention
The invention relates generally to gas lift arrangements used for enhanced recovery of hydrocarbons. In particular aspects, the invention relates to the construction and operation of gas lift valves used in hydrocarbon-producing wellbores.
2. Description of the Related Art
The flow of fluids into a wellbore from a surrounding subterranean reservoir often occurs as a result of natural formation pressure. This pressure is sometimes sufficient to lift oil within the wellbore to the surface for production. Sometimes, however, the formation pressure is not sufficient, and, even under the impetus of surface pumps, the rate of production is slow. In this case, techniques can be used to help improve the rate of production. One well-known technique for enhancing the rate of production is known as artificial lift, or gas lift. Gas lift valves are incorporated into the production tubing string and are used to flow high pressure natural gas from the annulus to the interior of the production tubing. The injected lighter gas provides a lift to the column of fluid within the production tubing to assist the flow of fluid from the well.
Gas lift valves must reliably provide for one-way fluid flow from the annulus to the interior of the tubing in order to prevent the undesirable leakage of production fluids into the annulus when the well is producing or closed in for maintenance or repair. Unfortunately, many conventional gas lift valve designs are prone to wear and damage during operation that can lead to seal failure and leakage over time. Conventional designs for gas lift valves usually incorporate a check dart or poppet member that is spring biased against a seat within the valve. Examples of valves having this type of construction are found in U.S. Pat. Nos. 6,932,581 and 6,715,550.
Flapper valves are known devices, but have been chiefly used as a safety valve mechanism within the flowbore of production tubing. Their function has been to prevent blowouts and emergencies by entirely closing off flow of fluid through the flowbore of a production tubing string. An example of a conventional flapper valve is shown in U.S. Pat. No. 6,705,593 issued to Deaton. To the inventors' knowledge, flapper mechanisms have not heretofore been incorporated into gas lift valves of any variety.
The present invention addresses the problems of the prior art.